This invention relates to power monitoring equipment of power derived from a motor-generator set, and more particularly, to a frequency detection circuit for maximizing the time before shutdown of the generator power upon detecting an impending power failure.
In systems which derive power from a public utility, various schemes are utilized in an attempt to isolate the system from interruption in the utility supplied power. One such isolation scheme interposes a motor-generator set between the utility supplied power and a power supply which generates supply voltages required by the system. When the utility supplied power delivered to the motor is interrupted, the inertia of the motor-generator set is sufficient to permit operation through a short term interruption or to allow a period of time to bring the system to an orderly halt, so that upon restoration of the utility supplied power the system can proceed without any special recovery procedures. The need for such an orderly halt is especially true in a data processing system.
In present systems, the motor-generator design can incorporate a timer that removes excitation from the generator after a fixed period of time from the time in which the utility supplied power (or primary power) interruption occurs. The timer time-out period is selected based on the generator frequency decay under full load conditions. As a result, such present designs may not fully utilize the available "ridethrough energy" especially under partially loaded conditions. (The "ridethrough energy" is the energy stored in the fly wheel, or inertia, of the motor-generator set.)
The present invention incorporates a generator shutdown scheme based on sensing or monitoring the generator frequency. The generator excitation is not removed until the sensed generator frequency has fallen below a detected predetermined value, the predetermined value being the threshold frequency at which the power supplies cannot properly generate and regulate the supply voltages to the system.
Accordingly, it is an object of the present invention to provide a device for sensing frequency.
It is another object of the present invention to provide a device for making full utilization of stored energy under all load conditions.
It is a further object of the present invention to provide a device for accurately sensing frequency so that shutdown can be co-ordinated with other events that are initiated by frequency sensing.
These and other objects of the present invention will become more apparent when taken in conjunction with the following description and attached drawings, wherein like characters indicate like parts, and which drawings form a part of the present application.